1. Field of the Invention
The present invention relates to a heat dissipation fan, and more particularly to a heat dissipation fan with low power loss.
2. Description of Related Art
With reference to FIG. 4, a conventional heat dissipation fan in accordance with the prior art comprises a casing (40), a stator (50) and a fan (60). The combination of the stator (40) and the fan (60) constitute a motor with the fan (60) serving as a rotor for the motor. The casing includes a sleeve (54) secured in the casing (40). The stator (50) is pressed onto the sleeve (54). The stator (50) has a coil (53), two pole disks (51,52) and a circuit board (55). The coil (53) has two sides, and the two pole disks (51, 52) respectively abut opposite sides of the coil (53). The circuit board (55) is securely attached to the stator (50) and is electrically connected to the coil (53).
The fan (60) is rotatably mounted in the stator (50) inside the casing (40). A permanent magnet (63) is securely mounted in the fan (60) to make the fan (60) the motor rotor. The fan (60) rotates due to the interaction between the magnetic forces in stator (50) and the permanent magnet (63). A low-friction member (541) like a lubricating bushing or a ball bearing is pressed into the sleeve (54). A shaft (64) securely attached to the fan (60) extends from the fan (60) and passes through a passage (not numbered) defined axially through the low-friction member (541). A neck (not numbered) is defined near the free end of the shaft (64). A locking disk (542) is mounted in the neck to securely hold the shaft (64) in the low-friction member (541).
Because there is a gap defined between the low-friction member (541) and the locking disk (542) and another gap defined between the low-friction member (541) and the fan (60), the shaft (64) will move up and down in the passage in the low-friction member (541) when the heat dissipation fan is in operation. The axial movement of the shaft (64) in the passage causes power loss in the fan motor.
To overcome the shortcomings, the present invention provides an improved heat dissipation fan to mitigate or obviate the aforementioned problems.
The main objective of the invention is to provide an improved heat dissipation fan that has low power loss. The heat dissipation fan has a casing, a stator and a fan. The combination of the stator and the fan constitutes a motor with the fan serving as a rotor for the motor. The casing includes a sleeve secured in the casing. The stator is pressed onto the sleeve inside the casing. The stator has a coil, two pole disks and a circuit board. The two pole disks respectively abut opposite sides of the coil. A low-friction member is mounted in the sleeve. The fan is rotatably mounted in the stator inside the casing. A permanent magnet is securely mounted in the fan to make the fan the motor rotor. A shaft securely attached to the fan extends from the fan and passes through the low-friction member. The permanent magnet and the coil in the stator have fixed heights. The height of the permanent magnet is smaller than that of the coil. The permanent magnet has a horizontal central line displaced axially from a horizontal central line of the coil of the stator. With such an arrangement, the fan will not move relative to the low-friction member due to the magnetic attraction provided by the coil on the permanent magnet. The fan with the shaft will not move axially during the operation of the heat dissipation fan. Consequently there is no power loss due to axial movement of the shaft in the low-friction member.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.